The present invention relates to a gear synchronizer assembly for power transmissions, and more particularly, but not exclusively, to a gear synchronizer mechanism of the type which comprises a gear member rotatable on a transmission shaft, a spline piece formed at one side thereof with a conical portion and thereon with external splines and mounted on a hub portion of the gear member for rotation therewith, a synchronizer ring mounted on the spline piece conical portion and cooperatable with the same for frictional engagement therewith in its shifted position, a hub member formed thereon with external splines and fixed to the shaft for rotation therewith, a clutch sleeve encircling the hub member and having internal splines in continual engagement with the external splines of the hub member, the clutch sleeve being axially shiftable to be engaged at the internal splines thereof with the external splines of the spline piece, and a thrust mechanism for moving the synchronizer ring toward the spline piece in shifting operation of the clutch sleeve to effect the frictional engagement between the synchronizer ring and the spline piece.
In such a conventional gear synchronizer mechanism as described above, the thrust mechanism comprises a plurality of circumferentially spaced strut keys each having a raised portion in engagement with a corresponding recess in the inner peripheral wall of the clutch sleeve, and a circular retainer spring arranged to bias the strut keys radially outwardly for engagement with the clutch sleeve. To simplify the construction and manufacturing process of the thrust mechanism, an improved thrust mechanism has been proposed in Japanese Early Patent Publications Nos. 55-100428, 58-137627, 58-163829, and 58-174724, wherein the strut keys and retainer springs are replaced with a single thrust element. It is, however, difficult to enhance productivity of the gear synchronizer mechanism because the single thrust element is complicated in its configuration and construction.